This is the first revision of a Phase I STTR proposal. This proposal aims to develop a tissue-based genetic test for BRCA2 hereditary breast cancer using a tissue-based IHC method. It is important to know which breast cancer patients have BRCA2 hereditary breast cancer because BRCA2 patients have an increased risk of breast cancer and their relatives with mutations have an increased risk of breast and ovarian cancer. These subsequent cancers would be discovered early or prevented if widespread genetic screening was available. We have developed an antibodybased tissue truncation method to identify BRCA2 hereditary cancers and have demonstrated the proof of concept for this technology. This approach visualizes protein truncation by showing with immunohistochemistry (IHC) that the N-terminus is present but the C-terminus is absent. Preliminary Data shows that 3 breast cancers with BRCA2 truncating mutations have truncated proteins by IHC while 20 sporadic breast cancers have full-length proteins detected by both N- and C-terminal antibodies. This project will fund research and development which will ultimately lead to a Phase II large clinical study of appropriate size to convince the FDA and the medical community that this test can efficiently and effectively identify patients with hereditary BRCA2 breast cancer. The product (test) will be an antibody-based IHC diagnostic kit for cancer tissue samples which hospital labs will use to identify hereditary cancers. The milestones for the Phase I proposal are: 1) Determine optimal tissue preparation protocols for IHC with both N-terminal and C-terminal BRCA2 antibodies. 2) Develop a quantitative scoring system for N- terminal and C-terminal BRCA2 immunostaining on ovarian tissues with intra-assay variability of 10% and inter-assay variability of 15% or less. 3) Demonstrate that a C-terminal to N-terminal ratio for protein truncation (BRCA2 Truncation Ratio) can distinguish 20 hereditary BRCA2 breast cancers from 50 sporadic breast cases with greater than 90% sensitivity and specificity (comparing different scoring systems). 4) Develop tissue based methods for PCR-sequencing to validate results of IHC studies using the sequencing benchmark. The goal of this Phase I proposal is to develop technology for a Phase II proposal to determine if the BRCA2 truncation test can achieve 90% sensitivity and specificity in a clinical trial of 500 breast cancer samples (sample size to provide 30 BRCA2 hereditary cancers). Breast Cancer relevance: Successful completion of this Phase I research would lead to a Phase II clinical trial which could establish a new tissue-based genetic test for BRCA2 hereditary breast cancer based on an IHC method to visualize protein truncation. This simpler more widely applicable approach will identify many more families with hereditary breast and ovarian cancer and consequently help patients and their relatives by identifying individuals likely to develop subsequent breast or ovarian cancer which might be prevented by tamoxifen and/or screening exams and X-rays. [unreadable] [unreadable] [unreadable]